On 2002-06-24 10:47, "ext Patrick Stickler" <patrick.stickler@nokia.com>
wrote:
>
> On 2002-06-21 15:53, "ext Jonathan Borden" <jonathan@openhealth.org> wrote:
>
>> The concept of "dark triples" as a layering option seems to be getting a bit
>> misunderstood. The essence of "dark" or "unasserted" triples is simply that,
>> from a technical perspective, it is difficult (some would indeed say
>> impossible) to define a language such as OWL (and given the constraints
>> placed on this language by the WebOnt charter etc.) in RDF if OWL is to have
>> the characteristics we desire, and RDF triples are all "truths".
>
> I consider RDF to already have a mechanism for expressing unasserted
> triples, namely reification. The only reason folks want to create something
> else, IMO, is simply because the RDF/XML syntax is so obese. I.e.
>
> <rdf:Statement>
> <rdf:subject rdf:resource="#foo"/>
> <rdf:predicate rdf:resource="&owl;bar"/>
> <rdf:object rdf:resource="#bas"/>
> </rdf:Statement>
>
> It seems to me that the solution is simply to add a contracted form
> of reification, to make the existing mechanism more palatable. E.g.
>
> <rdf:Statement rdf:about="#foo">
> <owl:bar rdf:resource="#bas"/>
> </rdf:Statement>
>
> Yes, this is a (minor) change to RDF/XML parsing, but IMO a far
> cheaper cost than any of the other proposals on the table for
> signaling "dark" triples. Note that it does not constitute a
> change to the RDF syntax, only to the special interpretation
> of rdf:Statement in contracted rather than full form. I.e it's
> only a change to the RDF/XML parsing algorithm. And since all
> RDF parsers are going to *have* to be revised to support the
> already adopted changes to RDF/XML, this is not a big deal.
>
> What more does OWL (or any other layer) need? An OWL application is
> then free to treat unasserted RDF statements employing OWL predicates,
> as asserted at the OWL layer, without any impact at all to RDF-only
> applications and without requiring RDF-only applications to know
> anything about any higher layers or (most importantly) needing to
> explicitly know which predicates in otherwise RDF asserted triples
> are "dark" and must actually be treated as unasserted at the
> RDF layer (what nonsense).
>
> Regards,
>
> Patrick
>
> --
>
> Patrick Stickler Phone: +358 50 483 9453
> Senior Research Scientist Fax: +358 7180 35409
> Nokia Research Center Email: patrick.stickler@nokia.com
Note also that unasserted "dark" statements at the RDF-level can be
asserted at any given higher level where they have meaning in a automated
and generic fashion.
OWL level assertions can be easily automated using this approach
by a single rule:
{
?x rdf:type rdf:Statement .
?x rdf:subject ?s .
?x rdf:predicate ?p .
?x rdf:object ?o .
?p rdf:type owl:OWLPredicate .
}
log:implies
{
?s ?p ?o .
}
Done.
This, of course, presumes that all OWL predicates are typed
as owl:OWLPredicate, but that's pretty cheap.
Higher layers built on top of OWL can just inherit OWLs
layer specific assertion rule as above, in addition to
their own.
Cheers,
Patrick
--
Patrick Stickler Phone: +358 50 483 9453
Senior Research Scientist Fax: +358 7180 35409
Nokia Research Center Email: patrick.stickler@nokia.com